The invention relates in general to bearings for supporting shafts for rotation and in particular to an improved structure for a center bearing assembly for rotatably supporting an intermediate portion of a vehicle drive line or coupling shaft assembly.
In most rear wheel drive vehicles, a source of rotational energy, such as an internal combustion or diesel engine, is located near the front of the vehicle. The engine is connected by means of a drive line to rotate one or more driven wheels located near the rear of the vehicle. The drive line typically extends between a transmission, which is connected to the engine, and a differential, which is connected to the driven wheels. In some vehicles, the distance separating the transmission and the differential is relatively short. In these vehicles, the drive line is composed of a single tube, usually referred to as the drive shaft. In other vehicles, the distance separating the transmission and the differential is relatively long, making the use of a single drive shaft impractical. In these vehicles, the drive line is composed of a drive shaft and one or more coupling shafts. The coupling shafts are connected to the drive shaft (and to each other) by universal joints.
Drive lines that are composed of a drive shaft and one or more coupling shafts require the use of one or more intermediate resilient support structures, which are generally referred to as center bearing assemblies or shaft support bearing assemblies. A typical center bearing assembly includes an annular roller bearing within which the coupling shaft is rotatably supported. The roller bearing itself is disposed within a generally annular resilient support member. The resilient support member is, in turn, disposed within a relatively rigid, generally U-shaped bracket which is secured to a cross member extending between the side rails of the vehicle frame.
The resilient support member is provided to reduce vibrations of the drive line in the vicinity of the center bearing assembly and to prevent such vibrations from being transmitted to the vehicle frame. In the past, the resilient support member has been formed from an elastomeric material, such as rubber. Under most vehicle operating conditions, known rubber support members are effective in substantially reducing the transmission of vibrations from the drive line to the vehicle frame. However, the vibration dampening characteristics of such known support members, which depend upon the specific material and the particular configuration thereof, remain constant regardless of the vehicle operating conditions. Accordingly, the vibration dampening characteristics of known support members can be optimized only for a single set of operating conditions. The vibrations generated by the drive line, on the other hand, constantly change with changes in the operating conditions of the vehicle. As a result, these support members may not provide optimum vibration dampening of vibrations under varying operating conditions. Vibrations generated by the vehicle and drive line also result in axial and radial movement of the roller bearing which receives the coupling shaft. In particular, the roller bearing is exposed to axial and radial movements transmitted from the coupling shaft. Such movements can be particularly objectionable during start up of a drive line.
It is desirable to provide an improved structure for a center bearing assembly which includes a support member having vibration dampening characteristics which can be adjusted in accordance with the changing operating conditions of the vehicle. Furthermore, it is desirable to provide an improved structure for a center bearing assembly which can accommodate axial and radial movements of the roller bearing during operation of the vehicle.